search param unipick with default "choose" : dont let users run the search with that value

[aurreco-uga]

happens in genes by location and the wgcna search. maybe others.

[ryanrdoherty]

Probably want an indicator from the backend that the client should treat the first choice as invalid. We could use a propertyList value but would probably be easier long term to just have an attribute like "disallowFirstOptionSelection=true" on the enum params we want this on, where default is false. Then we could check on both backend and frontend.